As a conventional conductive paste for use in electronic parts, such as internal electrodes of laminated capacitors, conductive patterns of circuit boards, and electrodes of substrates for plasma display panels, there is used a silver paste produced by kneading a mixture obtained by adding a silver powder and a glass frit to an organic vehicle. Such a silver paste is applied on a substrate and dried, and then, it is fired to form a conductive pattern.
In recent years, such electronic parts are miniaturized, so that it is required that a silver powder for a conductive paste has a reasonably small particle size and a reasonably narrow range of the particle size in order to form conductive patterns having a high density and fine lines.
As a method for producing such a silver powder for a conductive paste, there is known a method for adding an alkali or a complexing agent to an aqueous silver-salt containing solution to form a silver oxide containing slurry or an aqueous silver-complex-salt containing solution, and then, adding a reducing agent to the slurry or solution to deposit a silver powder by wet reduction.
However, there is a problem in that a silver powder produced by such a conventional method is not able to be applied to recent electronic parts, such as fine-line conductive patterns, internal electrodes of laminated capacitors, and electrodes of substrates for plasma display panels, since the silver powder is violently aggregated.
For that reason, in order to form a silver powder having small amount of aggregates and good dispersibility, there is proposed a method for forming a silver powder by adding a dispersing agent, which is at least one of fatty acids, fatty acid salts, surfactants, organic metals and protective colloids, to a silver containing slurry, which is obtained by adding an alkali or a complexing agent to an aqueous silver-salt containing solution to form a silver oxide containing slurry or an aqueous silver-complex-salt containing solution, and then, adding a reducing agent to the slurry or solution to deposit silver particles by wet reduction (see, e.g., Patent Document 1).